Method for processing manure, fermented manure and ammonium nitrogen containing waste water

ABSTRACT

The invention relates to a method for processing manure, fermented liquid manure being subjected to nitrification in a first step and to denitrification in a subsequent step, an aerated reactor which contains active sludge rich in nitrifying bacteria being used in the nitrification step and acid-neutralizing chemicals being added to said reactor if necessary and a continuously fed upflow sludge bed (USB) reactor which contains a very compact biomass which is capable of converting nitrate to nitrogen gas and to which an organic substrate is added being used in the denitrification step, the loading of the reactor being controlled to obtain an optimum nitrification and denitrification and this is obtained on the basis of one or more of the following data: 
     the incoming nitrogen load; 
     the information from the WAZU respiration meter; 
     the pH in the nitrification reactor, the criterion for which is that the pH is in the range limited by 6 and 8.5; 
     the temperature in both the nitrification reactor and the denitrification reactor is kept below 40° C.; 
     the concentration of oxidized nitrogen in the influent for the denitrification reactor, the criterion for which is that the concentration is between 0 and 4 g N/l; 
     the concentration of oxidized nitrogen in the nitrification reactor, the criterion for which in the sludge/liquid mixture in the reactor is that the concentration is between 0 and 4 g N/l; 
     the concentration of the carbon source in the effluent from the denitrification reactor; 
     the gas production in the denitrification reactor. The invention further relates to an apparatus for performing this method comprising at least one WAZU respirator meter.

This is a division of U.S. patent application Ser. No. 07/599,345, filedOct. 17, 1990, U.S. Pat. No. 5,232,583.

BACKGROUND OF THE INVENTION

The present invention relates to a method for processing manure,fermented manure or waste water having a relatively high ammonianitrogen concentration, said liquid manure being subjected tonitrification in a first step and to denitrification in a subsequentstep, an aerated reactor which contains active sludge rich in nitrifyingbacteria being used in the nitrification step and acid-neutralizingchemicals being added to said reactor if necessary and a continuouslyfed upflow sludge bed (USB) reactor which contains a very compactbiomass which is capable of converting nitrate to nitrogen gas and towhich an organic substrate is added for use in the denitrification step.

A method of this type is known from, inter alia, Agrarisch Dagblad ofMar. 14, 1988. With this method the liquid fraction of fermentedsemi-liquid manure is treated. The biologically degradable organicsubstances, nitrifiable nitrogen and phosphorus which are present in theliquid fraction of anaerobic or fermented semi-liquid manure can belargely removed. The method essentially consists in a coupling of anitrification step in a nitrification reactor in which ammonia isconverted by bacteria to oxidized nitrogen with a denitrification stepin a denitrification reactor in which oxidized nitrogen is converted bybacteria to nitrogen gas, the phosphate present in the liquid beingconcentrated as a chemical precipitate in the reactor at the same time.Oxidation of ammonia results in lowering of the pH, which, with thismethod, can be countered by metering in lime and/or metering in effluentfrom the denitrification reactor (recycling) to the nitrificationreactor. During the nitrification step of this method there will also besome removal of nitrogen and phosphate since the bacteria degradebiologically degradable substances which have passed through thefermentation to give CO₂ and H₂ O. The nitrogen and phosphorus thusliberated can be incorporated in the new cells of the active sludge.With this method the nitrification reactor (which can be either a fedbatch reactor or a batch reactor) is operated batchwise. It is thenaerated until all ammonia has been nitrified, after which the aerationis stopped temporarily in order to allow the sludge to settle. Thenitrified liquid manure is run off for treatment in the denitrificationstep, while the active sludge remains behind in the nitrificationreactor for a subsequent cycle. In the denitrification step the effluentfrom the nitrification reactor is pumped upwards through a USB (upflowsludge bed) reactor. In this reactor there is a very compact biomasswhich is capable of converting nitrate to nitrogen gas. In order toallow this step to proceed, an organic substrate--for examplemethanol--must be added to the reactor. Acid is consumed during thedenitrification step, as a result of which the pH in the bacterial bedrises. As a consequence of this rise, an insoluble precipitate ofphosphate, with the calcium ions present in the liquid, forms. Themanure processing consisting of manure fermentation and separation offermented manure, followed by the method for treatment of the liquidfraction of fermented semi-liquid manure, which has been describedabove, and is shown in FIG. 1.

A number of manure processing works are being developed at present, forexample Promest in Helmond and Memon in Deventer. In these workssemi-liquid manure is evaporated to give a dry product, which costs agreat deal of energy since semi-liquid manure consists of more than 90%of water. Moreover, this evaporation is a complex technology which infact still has to be developed for use on manure. The cost price ofprocessing of this type for the formation of dry granular or powdermanure is consequently very high.

An approach which differs from that described above is the treatment ofsemi-liquid manure in conventional effluent treatment installations.Currently this is also being used for treatment of liquid manure fromcalves. The conventional manure treatment has the significantdisadvantages that the process produces a large amount of sludge (excessbacteria) and that the process is not capable of removing the phosphate.This means that extra provisions have to be made for sludge treatmentand dephosphating. A conventional manure treatment also requires afairly large amount of space.

This method, as reported in Agrarisch Dagblad of Mar. 17, 1988, has theadvantage that it is relatively inexpensive and can be carried out in acompact installation. However, a number of problems also arise in thiscase in the treatment of fermented manure.

A compact manure treatment installation for manure and fermented manureor ammonium nitrogen containing waste water can be produced andmaintained only if:

a) the metering of the fermented liquid fraction is matched to thenitrification capacity of the nitrification reactor. The nitrificationreactor must not be overloaded but must also not operate underloaded.

b) The metering of methanol (or other sources of carbon) to thedenitrification reactor is matched to the nitrate load in thedenitrification reactor. In the case of undermetering not all nitrate isremoved; in the case of overmetering, however, methanol (or other sourceof carbon) is present in the effluent to be discharged.

c) The effluent recycling from denitrification reactor to nitrificationreactor is controlled such that it is optimal. Too little recyclingleads to a nitrate concentration which has an inhibitory action on thebacteria; too much recycling has the consequence that the reactor isfilled mainly with liquid which has already been treated.

Said points can be achieved by the use of separate instruments, it beingnecessary to carry out some of the diverse operations by hand. Moreover,the results of the various measurements cannot be integrated andtranslated into a control action without the intervention of oneoperator. Furthermore, the effluent from the nitrification reactor canstill contain organic substances which cannot be further degraded in thenitrification reactor. Organic material which passes into thedenitrification reactor can be converted into inorganic material in thatreactor with the liberation of ammonium nitrogen which is then (insofaras it is not fed via the recycle stream) discharged with the effluent.

SUMMARY OF THE INVENTION

The aim of the present invention is to eliminate these problems. Thepresent invention relates to a method of the type indicated in thepreamble which is characterized in that the loading of the nitrificationreactor is controlled and the optimum nitrification and denitrificationare obtained on the basis of one or more of the following data:

the incoming nitrogen load;

the information from the WAZU respiration meter (Netherlands PatentApplication No. 8600396, filed on Feb. 17, 1986);

the pH in the nitrification reactor, the criterion for which is that itis in the range limited by 6 and 8.5 and preferably in the range of 6.5to 7.5;

the temperature in both the nitrification reactor and thedenitrification reactor, the criterion for which is that this is lowerthan 40° C. and preferably in the range of 25° C. to 35° C.;

the concentration of oxidized nitrogen in the influent for thedenitrification reactor, the criterion for which is that theconcentration is between 0 and 4 g N/l;

the concentration of oxidized nitrogen in the nitrification reactor, thecriterion for which in the sludge/liquid mixture in the reactor is thatthe concentration is between 0 and 4 g N/l;

the concentration of the carbon source in the effluent from thedenitrification reactor;

the gas production in the denitrification reactor.

In particular the present invention relates to a method of the typeindicated in the preamble which is characterized in that

a) the loading of the nitrification reactor is controlled to obtain anoptimum nitrification and denitrification, said optimum being obtainedon the basis of the following data:

the incoming nitrogen load (by controlling the fermented liquid manure);

the incoming oxygen load (by controlling aeration);

the information from the WAZU respiration meter or the information of anoxygen determination in the nitrification reactor;

the concentration of oxidized nitrogen in the nitrification reactor,said concentration in the sludge/liquid mixture in the reactor beingmaintained between 0 and 4 g N/l by adjusting one or more of the ratioof the influent flow (the fermented liquid manure), and therecirculation flow and

b) the loading of the denitrification reactor is controlled to obtain anoptimum denitrification, said optimum being obtained by:

maintaining the concentration of oxidized nitrogen in the influent forthe denitrification reactor between 0 and 4 g/N/l;

maintaining the incoming oxidized nitrogen load, below or equal to thenitrate removal capacity so the nitrate concentration in the effluent isbelow the allowable concentration, and optionally further controllingthe denitrification on the basis of one or more of the gas production inthe denitrification reactor and the nitrate effluent concentration;

supplying an amount of organic substrate calculated from one or more ofthe incoming oxidized nitrogen load, the gas production in thedenitrification reactor and the nitrate concentration of the effluent ofthe denitrification reactor, preferably from at least the incomingoxidized nitrogen load and

c) the temperature in both the nitrification reactor and thedenitrification reactor is maintained below 40° C. (preferably 25°C.-35° C.) and

d) the pH-value in the nitrification reactor is maintained in the rangeof 6 to 8.5 (preferably 6.5-7.5).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process flow schematic of the prior art process for a methodfor treatment of semi-liquid manure;

FIG. 2 illustrates a control schematic of the WAZU respiration meterutilized in an embodiment of the present invention;

FIG. 3 is a schematic illustrating a physical/chemical flocculation stepand separation of the floccule;

FIG. 4 illustrates a process flow schematic of a further embodiment ofthe present invention;

FIG. 5 illustrates a slightly modified, different embodiment of theprocess of the present invention similar to that illustrated in FIG. 4;

FIG. 6 illustrates a slightly modified, different embodiment of theprocess of the present invention similar to that illustrated in FIGS. 4and 5;

FIG. 7 illustrates a slightly modified, different embodiment of theprocess of the present invention similar to that illustrated in FIGS. 4,5 and 6;

FIG. 8 illustrates a slightly modified, different embodiment of theprocess of the present invention similar to that illustrated in FIGS.4-7;

FIG. 9 illustrates a slightly modified, different embodiment of theprocess of the present invention similar to that illustrated in FIGS.4-8;

FIG. 10 is a process flow schematic diagram illustrating in more detailthe preferred embodiment of the present invention;

FIG. 11 illustrates a process flow, mass balance schematic of theprocess of the present invention; and

FIG. 12 illustrates a process cycle for the process of the presentinvention, including a plot of dissolved oxygen versus time for a singletreatment cycle.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An important aspect of the invention is the use of one instrument, arespiration meter (WAZU respiration meter), with which the time at whichthe treatment processes are complete is established and with which bothammonium nitrogen concentration in the liquid fraction of fermentedmanure to be treated and the nitrate concentration of the effluent fromthe nitrification reactor (=feed for the denitrification reactor) can becalculated. The liquid streams and control lines in relation to therespiration meter are shown schematically in FIG. 2. As is apparent fromthe figure, the use of nitrogen gas production for controlling theamount of organic substrate to be metered is optional. It is possible touse solely the incoming oxidized nitrogen load to meter the amount oforganic substrate as can be seen where the control line runs from theincoming oxidized nitrogen line to the WAZU respiration meter. Theoption whereby the control line runs to the WAZU respiration meter fromthe nitrogen gas production is not indicated in the Figure. The scale ofthe plant will determine which option to use. For large scaleproduction, measurement of the nitrogen gas production is noteconomically feasible so preferably the incoming oxidized nitrogen loadwill be used. It is also possible to use both measurements. A personskilled in the art will be able to ascertain which option to use. Therespiration meter can control the entire method automatically on thebasis of the data collated and calculated by the instrument.

Another aspect of the invention is the use of a separation step, e.g. aphysical/chemical flocculation step and a floccule separator or amembrane technology before or after the denitrification step. Purpose ofsaid separation previous to the denitrification reactor is catchingsuspended and colloidally dissolved organic substances, that otherwisewould minerallize in the denitrification reactor resulting in theformation of ammoniun nitrogen. A physical/chemical flocculation stepplus floccule separation is shown schematically in FIG. 3. The residualorganic substance can be removed from the effluent with the aid offlocculating auxiliaries and a process for separation of the flocculantfrom the effluent. By positioning upstream of the denitrification step,the organic substances can be removed before they are converted toinorganic substances and ammonium nitrogen is formed. A furtheradvantage of this is that the carbonate content in the effluent from thenitrification reactor is low (lower than in the effluent from thedenitrification reactor, to which organic substrate is added). This isadvantageous if a flocculating auxiliary is used which forms aprecipitate with carbonate, such as, for example, iron chloride. If aflocculating auxiliary is used which contains cations which precipitatewith phosphate, an additional phosphate treatment takes place.

Furthermore, the optimum conditions for the present treatment methodshave been investigated in both the nitrification and the denitrificationreactor. The biomass in both the nitrification reactor and thedenitrification reactor produce heat. Because of the high concentrationof biomass and the high rates of conversion which are realized in bothreactors, there will be a net excess of heat in both reactors if nomeasures are taken. It is known, from observations made by the Applicantin laboratory experiments, that for a nitrifying bacterial populationthe optimum temperature of this bacterial population is between 31° and35° C. and that the maximum temperature which can be tolerated is 40° C.On the basis of general scientific information, it can be anticipatedthat the same temperature limits apply for the denitrifying bacterialpopulation. Thermophilic denitrifying bacteria are known. These operateat temperatures above about 50° C. However, for various reasons it isnot desirable to use thermophilic organisms in the denitrificationreactor: the effluent to be discharged will be much too warm and therecycle stream to the nitrification reactor may not be too warm. Boththe nitrification and the denitrification reactor can be operated onlyif there is provision for removal of heat from the respective reactorcontents. The temperature also influences the solubility of oxygen inwater. A higher temperature leads to lower solubility of oxygen andtherefore leads to increased need for aeration. Increased aeration canresult in undesirable foam formation, the amount of foam formation beingdependent, e.g., on protein content of the liquid to be treated.

For the present method, the conditions in the denitrification reactormust be kept such that phosphate can precipitate. The efficiency of thephosphate removal is dependent on the pH and the HCO₃ ⁻ /CO₃ ²⁻ ratio inthe denitrification reactor.

The desired pH can be obtained by using an organic C source for thedenitrification reactor with a specific chemical oxygen consumption(COC)/total organic carbon (TOC) ratio in the present method. The factis that alkalinity (alkali, bicarbonate and carbonate) is produced inthe denitrification reactor under the influence of the denitrificationreaction. The production of alkalinity is dependent on the COC/TOC ratioof the organic C source in the denitrification reaction. Usuallymethanol is used as organic C source. Methanol has a high COC/TOC ratioand results in a higher production of alkalinity than, for example,glucose, which has a much lower COC/TOC ratio. Experiments have shownthat the COC/TOC ratio must be 3.75 or more.

As stated, the pH value falls in the nitrification reactor on theoxidation of the ammonia. To counter acidification of the reactor, analkali can be metered in or effluent can be recycled from thedenitrification reactor to the nitrification reactor. It has beenestablished experimentally that the concentration of oxidized nitrogenin the nitrification reactor in the sludge/liquid mixture is between 0and 4 g N/l and preferably is in the range limited by 0 and 1.5 g N/l.Furthermore, it has been found that the concentration of oxidizednitrogen in the influent for the denitrification reactor is between 0and 4 g N/l and is preferably between 1.0 and 1.4 g N/l. In order toachieve this, the effluent from the denitrification reactor can berecycled. This recycling provides dilution of the concentration ofoxidized nitrogen at the feed location in the reactor. Furthermore, thisrecycling is intended to obtain a higher stream velocity in thedenitrification reactor, which promotes the contact between biomass andsubstrate in the reactor. Recycling can take place directly fromeffluent stream to influent stream for the denitrification reactor. Itis, however, also possible (and in fact better for the overall process)for recycling of effluent from the denitrification reactor to be used,this recycling taking place entirely or partially via the nitrificationreactor see, e.g., FIG. 5. The aim of this is then to achieve both asaving in the chemicals consumption for pH control in the nitrificationreactor and to achieve a dilution of the reactor contents of thenitrification reactor such that the content of oxidized nitrogen isalways lower than 4 g N/l.

The present invention also relates to an installation which is suitablefor carrying out the method as described above, comprising:

a nitrification reactor which is provided with an aeration, feed ofliquid to be treated, feed of acid-neutralizing chemicals, active sludgerich in nitrifying bacteria, a sludge discharge, an effluent discharge;

a line through which the effluent from the reactor can be fed to thedenitrification reactor;

a denitrification reactor which is provided with a feed of effluent fromthe nitrification reactor, feed of a carbon source, an upflow sludge bed(USB) column, a very compact biomass capable of converting nitrate tonitrogen gas, a discharge of phosphate-rich sludge discharge, aneffluent discharge, a nitrogen gas discharge;

a line through which the effluent from the denitrification reactor canbe discharged, which is characterized in that the installation (shownschematically in FIG. 2) is provided with one or more WAZU respirationmeters (18) controlling the aeration (10), the liquid supply to betreated (7), the sludge discharge (11) of the nitrification reactor andthe supply of the source of carbon (14).

In the most simple form, the installation (shown schematically in FIG.2) consists of the combination of a batch reactor (to which all influent(7) is added at once per cycle) or a fed batch reactor (to which theinfluent is added gradually or stepwise per cycle) as nitrificationreactor (9) and a continuously fed upflow slib bed (USB) reactor asdenitrification reactor (13). The two reactors are operated connected inseries, without bypass of the nitrification reactor (9) but optionallywith backmixing (33) from the denitrification reactor (13) to thenitrification reactor (9).

The use of the WAZU respiration meter (18) (Netherlands PatentApplication 86.00396, filed on Feb. 6, 1986 & EP-A 257057), ameasurement and control unit with which the course of the respirationrate of the biomass in the reactor (9) is followed, is characteristic ofthe installation according to the present invention.

The nitrification reactor (9) of the installation is provided withaeration (10), a feed of liquid (7) to be treated, a sludge discharge(11) and optically a feed of effluent from the denitrification reactor(33), all of which are controlled by the WAZU respiration meter (18)(Netherlands Patent Application 86.00396, filed on Feb. 6, 1986). Thisrespiration meter also controls the metering of the source of carbon(14) for the denitrification reactor (13). This denitrification reactoris additionally provided with nitrogen gas discharge (17) and effluentrecirculation (33) or discharge (16).

Another embodiment of the installation according to the invention (shownschematically in FIG. 4) is also provided with a line (32) through whichthe effluent from the denitrification reactor (13) can be partiallyrecycled to the influent (12) for the denitrification reactor (13) andadditionally this installation is provided with a feed of one or moreacid-neutralizing chemicals (8) to the nitrification reactor (9).

Furthermore, the installation can comprise a combination of the twoabove installations (FIGS. 4 and 5), i.e. an installation as shown inFIG. 6, this installation being provided with a line through which theeffluent (32, 33) from the denitrification reactor (13) can be partiallyrecycled (33 and 32 respectively) to the nitrification reactor (9) andto the influent (12) for the denitrification reactor (13).

The three lastmentioned installations, shown in FIGS. 4, 5 and 6, cancomprise a further addition (see FIG. 7) in the form of a feed ofchemicals for phosphate precipitation (20).

Furthermore, all of these installations (shown in FIGS. 4, 5, 6 and 7)can be provided with one or more flocculation installations (19). Theflocculation installation as such is shown schematically in FIG. 3.

FIG. 3, an influent pump 26 feeds into a static mixer and/orflocculating tank 27. An iron chloride storage tank 30 feeds a meteringpump 31, which in turn supplies a metered amount of iron chloride intotank 27. Tank 27 is feedably connected into a centrifuge 28. Centrifuge28 has an outlet indicated by the upwardly directed arrow and a secondoutlet connected to sludge pump 29. The output of sludge pump 29 isindicated by a downwardly connected arrow.

The installations according to the invention which have already beendescribed can be provided with the flocculation installations at variouslocations (FIGS. 8, 9 and 10). In the installation according to FIG. 8,the flocculation installation (19) is positioned in such a way that theeffluent (16) from the denitrification reactor (13) flows through theflocculation installation (19), shown in detail in FIG. 3 upstream ofthe recycle (34, 35) or discharge (16).

In the installation according to FIG. 9, the flocculation installation(19) is positioned in such a way that only the effluent (16) from thedenitrification reactor (13) which is to be discharged flows through theflocculation installation (19).

In the installation according to FIG. 10, which is preferred, theflocculation installation (19) is positioned in such a way that theeffluent (12) originating from the nitrification reactor (9) flowsthrough the flocculation installation (19) before it flows into thedenitrification reactor (13).

The installations according to the invention in which the nitrificationreactor is provided with feed of the effluent (16, 33, 34) from thedenitrification reactor (13) can be provided with a spray installation(25 and FIG. 10) through which the effluent (16, 33, 34) from thedenitrification reactor (13) can be sprayed into the nitrificationreactor (9) to prevent foam formation.

Furthermore, all installations according to the invention can beprovided with one or more buffer tanks (23 and FIG. 10). The examplesgiven serve to illustrate the invention and must not be regarded asrestrictive.

EXPLANATION OF THE NUMERALS IN THE FIGURES

1. Storage of semi-liquid manure

2. Fermentation installation

3. Biogas

4. Installation for energy generation

5. Installation for mechanical separation

6. Cake

7. Filtrate=liquid fraction to be treated

8. Holder for metering acid-neutralizing chemicals

9. Nitrification reactor

10. Air supply

11. Sludge discharge

12. Effluent from the nitrification reactor

13. Denitrification reactor

14. Holder for metering C source

15. Phosphate-rich sludge

16. Effluent from the denitrification reactor

17. Nitrogen gas

18. WAZU respiration meter

19. Separation installation

20. Holder for chemicals for phosphate precipitation

21. Sludge, flocculated material

22. Effluent originating from the flocculation installation, positioneddownstream of the denitrification reactor

23. Buffer tank

24. Storage of discharged sludge

25. Spray installation

26. Influent pump

27. Static mixer and/or flocculating tank

28. Centrifuge

29. Sludge pump

30. Iron chloride storage

31. Metering pump

32. Effluent originating from the denitrification reactor which recyclesto the denitrification reactor

33. Effluent originating from the denitrification reactor which recyclesto the nitrification reactor

34. Effluent originating from the separation step, which is positioneddownstream of the denitrification reactor, which flows to thenitrification reactor

35. Effluent originating from the separation step, which is positioneddownstream of the denitrification reactor, which recycles to thenitrification reactor

36. Effluent originating from the separation step, which is positionedupstream of the denitrification reactor.

37. Effluent from buffer tank (23).

A possible embodiment of the present invention, not limiting the scopeof the invention, is illustrated by means of the following example.

EXAMPLE

Fermented manure (i.e., the liquid fraction obtained by centrifugationof anaerobic fermented floating pig manure) is treated in the apparatusshown in FIG. 11 consisting of a nitrification reactor (9) having ausable volume of 50 m³, a separator (19) consisting of a pipeflocculator (27) and a centrifuge (28) and two denitrification reactorswhich are positioned parallel to each other each having a usable sludgebed volume of 10 m³.

The nitrification reactor in this example is a fed batch reactor with astepwise addition (0.2 m³ of manure per step) of fermented manure. Atotal of 2 m³ of manure is added in ten steps.

In the total cyclus of the nitrification reactor 8 m³ of effluent of thedenitrification reactor is supplied proportionally distributed in thetime. After a total of 2 m³ fermented manure has been introduced in anitrification reactor and all ammonium nitrogen has been nitrificated,the aeration is ended and the active sludge is allowed to sedimentduring sixty minutes. After the sedimentation period, 10 m³ of thesupernatant liquid is discarded as an effluent of the nitrificationreactor. Then a new cyclus is started wherein again 2 m³ of fermentedmanure and 8 m³ of effluent of the denitrification reactor are added,

A WAZU respiration meter (trademark RA-1000; marketed by Manotherm) iscoupled to the nitrification reactor to monitor the actual respirationvelocity. Further, the oxygen concentration in the nitrification reactoris monitored with an oxygen sensor.

After the addition of 0.2 m³ of fermented manure the actual respirationvelocity increases and the oxygen concentration in the nitrificationreactor decreases. When the ammonium hydrogen added with the fermentedmanure is nitrificated the actual respiration velocity decreases to thebasis level and the oxygen concentration in the nitrification reactorincreases. After falling underneath the set point for the respirationvelocity and/or exceeding of the set point of the oxygen concentration,another 0.2 m³ of fermented manure is added to the nitrificationreactor. FIG. 12 gives the oxygen concentration in the nitrificationreactor as a function of the time. The average dose of the fermentedmanure in the present nitrification reactor was in this test about 10 m³a day.

The pH-value is also measured in the nitrification reactor. Lime milk issupplied when the pH-value is below 6.5.

The temperature is also monitored and is kept at a value below 33° C. bymeans of a heat exchanger.

From the oxygen consumption of the substrate during a cyclus (thecumulative actual respiration velocity minus the cumulative basisrespiration velocity) it can be calculated that the concentration ofnitrificible nitrogen in the fermented manure is 6000 mg N/l. Theeffluent of the nitrification reactor has a nitrate-N concentration of1100 mg N/l and a phosphate-P concentration of 25 mg P/l. The nitrogen-Nconcentration is lower than could be expected on the basis of thedilution of the reactor contents with effluent of the denitrificationreactor. This is the consequence of some denitrification in thenitrification reactor during the sedimentation period and theincorporation of nitrogen in the biomass.

The effluent of the nitrification reactor is pumped through a pipeflocculator. At the beginning of this flocculator a 41 w. %(weight/weight) solution of FeCl₃ (ferric chloride, iron trichloride) isdosed in an amount of 2.5 l per m³ effluent of the nitrificationreactor. In the middle of the pipe flocculator lime milk and/or causticsoda is supplied until the pH-value has reached 5.8. At the end of thepipe flocculator polyelectrolyte is dosed (76 mg per m³ effluent of thenitrification reactor). The liquid then passes through a centrifugeseparating in a sludge stream and a liquid stream. The nitrate-N andphosphate-P concentration in the effluent of the centrifuge amount 1100mg N/l and <0.5 mg P/l, respectively.

The effluent of the centrifuge is then put through the twodenitrification reactors that have been arranged parallel. Methanol isadded on the basis of the nitrate concentration in the influent stream.The denitrification process is monitored by means of the gas production(1850 l/h). The pH-value of the denitrification reactors is between 9.0and 9.3. The temperature is kept below 35° C. by means of a heatexchanger. The effluent of the denitrification reactors is recirculatedfor 80% and discharged for 20%. Analysis shows a nitrate-Nconcentration<10 mg N/l and a phosphate-P concentration of <0.5 mg P/l.

Table A shows the quality of the fermented manure before and aftertreatment in the present apparatus.

                  TABLE A                                                         ______________________________________                                               in         out      yield                                                     (mg/l)     (mg/l)   %                                                  ______________________________________                                        COD      15,000       300-900   94-98                                         N         6,000        0-10    99.8-100                                       P          275          0-0,2  99.9-100                                       ______________________________________                                    

Table B illustrates the quality of the effluent obtained.

                  TABLE B                                                         ______________________________________                                        COD                 300-900   mg/l                                            BOD                 0-10                                                      nitrate             0-10                                                      ammonium            0                                                         phosphate           0-0,2                                                     chloride            2200                                                      pesticides                                                                    PAK                                                                           EOCl                    cannot be detected                                    AOX                                                                           ______________________________________                                    

We claim:
 1. Method for processing manure, wherein fermented liquidmanure is subjected to nitrification in a first step in an aeratednitrification reactor containing active sludge rich in nitrifyingbacteria used in the nitrification step, acid-neutralizing chemicalsbeing added to said nitrification reactor if necessary, and the effluentof the liquid manure from the nitrification reactor is then subjected todentrification in a subsequent step in a continuously fed upflow sludgebed denitrification reactor containing a very compact biomass which iscapable of converting nitrate to nitrogen gas and to which an organicsubstrate is added for use in the denitrification step, wherein theloading of the nitrification reactor is controlled to obtain optimalnitrification and denitrification on the basis of at least one of thefollowing data:the incoming nitrogen load; the information from a WAZUrespiration meter; the oxygen concentration in the nitrificationreactor; the pH in the nitrification reactor being maintained in a rangeof from about 6 to about 8.5; the temperature in both the nitrificationreactor and the denitrification reactor being kept below 40° C.; theconcentration of oxidized nitrogen in the influent for thedenitrification reactor being between 0 and 4 g N/l; the concentrationof oxidized nitrogen in the sludge/liquid mixture in the nitrificationreactor being between 0 and 4 g N/l; the concentration of the carbonsource in the effluent from the denitrification reactor; and/or the gasproduction in the denitrification reactor.
 2. Method according to claim1, wherein the effluent from the nitrification reactor is first passedthrough a physical/chemical flocculation installation.
 3. Methodaccording to claim 2, wherein the flocculating substance used is asubstance which contains cations which can precipitate with phosphate.4. Method according to claim 3, wherein iron chloride is used as aflocculating substance.
 5. Method according to claim 2, wherein part ofthe effluent after denitrification is recycled into the effluent fromthe nitrification reactor before this flows into the denitrificationreactor.
 6. Method according to claim 1, wherein liquid is recycled fromthe reactor where denitrification takes place to the nitrificationreactor where nitrification takes place.
 7. Method according to claim 6,wherein the recycled liquid is passed through a spray installationbefore the liquid reaches the nitrification reactor.
 8. Method accordingto claim 1, wherein the nitrification reactor used is a batch reactor.9. Method according to claim 1, wherein chemicals for phosphateprecipitation are added to the denitrification reactor.
 10. Methodaccording to claim 9, wherein at least one of the chemicals forphosphate precipitation is selected from the group consisting of: Ca²⁺,Fe³⁺, Mg²⁺ and Al³⁺.
 11. Method according to claim 1, wherein methanolis added as organic substrate to the denitrification reactor.
 12. Methodaccording to claim 1, wherein glycol is added as organic substrate tothe denitrification reactor.
 13. Method according to claim 1, in whichan organic substance or a mixture of organic substances is added to thedenitrification reactor, wherein the ratio between chemical oxygenconsumption and total organic carbon (COC/TOC ratio) of more than orequal to 3.75 is maintained.
 14. Method according to claim 1, wherein atleast one acid-neutralizing chemical is added to the nitrificationreactor.
 15. Method according to claim 14, wherein lime is added. 16.Method according to claim 1, wherein the concentration of oxidizednitrogen in the influent for the dentrification reactor is maintained atfrom about 1.0 to about 1.4 g N/l.
 17. Method according to claim 1,wherein the concentration of oxidized nitrogen in the nitrificationreactor is maintained at from about 0 to about 1.5 g N/l.
 18. Method forprocessing manure, wherein fermented liquid manure is subjected tonitrification in a first step in an aerated nitrification reactorcontaining active sludge rich in nitrifying bacteria, acid-neutralizingchemicals being added to said nitrification reactor if necessary, andthe effluent of the liquid manure from the nitrification reactor is thensubjected to denitrification in a subsequent step in a continuously fedupflow sludge bed denitrification reactor containing a very compactbiomass for converting nitrate to nitrogen gas and to which an organicsubstrate is added, the temperature in both the nitrification reactorand the dentrification reactor being kept below 40° C. and the pH in thenitrification reactor being maintained in a range from about 6 to about8.5;wherein the loading of the nitrification reactor is controlled toobtain optimal nitrification and denitrification on the basis of thefollowing parameters: the incoming nitrogen load by controlling thefermented liquid manure; the incoming oxygen load by controllingaeration; the information from a WAZU respiration meter or the oxygenconcentration in the nitrification reactor; maintaining theconcentration of oxidized nitrogen in the sludge/liquid mixture in thenitrification reactor between 0 and 4 g N/l; and wherein the loading ofthe denitrification reactor is controlled to obtain optimaldenitrification on the basis of the following parameters: maintainingthe concentration of oxidized nitrogen in the the influent for thedenitrification reactor between 0 and 4 g N/l; maintaining the incomingoxidized nitrogen load below or equal to the nitrate removal capacity sothe nitrate concentration in the effluent from the nitrification reactoris below 4 g N/l; the amount of the organic substrate added beingcalculated on the basis of at least one of the incoming oxidizednitrogen load, the gas production in the denitrification reactor ornitrate effluent concentration.
 19. Method according to claim 18,wherein the concentration of oxidized nitrogen in the sludge/liquidmixture in the nitrification reactor is maintained between 0 and 4 g N/lby adjusting the ratio of the influent flow of fermented liquid manureand/or by adjusting the recirculation flow.
 20. Method according toclaim 18, wherein the amount of the organic substrate added iscalculated on the basis of the incoming oxidized nitrogen load. 21.Method according to claim 18, wherein the loading of the denitrificationreactor is further controlled to obtain optimal denitrification on thebasis of monitoring the nitrate removal on the basis of at least one ofthe gas production in the denitrification reactor and/or the nitrateeffluent concentration.